Collapsible stool



FIG. 1 is a perspective top front right view of a collapsible stool, showing my new design;

FIG. 2 is a perspective top rear left view thereof;

FIG. 3 is a front elevation view thereof;

FIG. 4 is a rear elevation view thereof;

FIG. 5 is a right elevation view thereof;

FIG. 6 is a left elevation view thereof;

FIG. 7 is a top plan view thereof; and,

FIG. 8 is a bottom plan view thereof. 

CLAIM The ornamental design for a collapsible stool, as shown and described. 